In this study, experimental studies were conducted in order to promote a practical use of sand pre-mixed with fly-ash. The measuring method of the fly-ash content of sand pre-mixed with fly-ash were examined, and the influence of fly-ash content fluctuations of sand pre-mixed with fly-ash on measurement of surface water and properties of concrete using sand pre-mixed with fly-ash. From these experimental studies, it was confirmed that fly-ash content of sand pre-mixed with fly-ash can be measured by measuring the amount of fine particles passing through the tests sieve 75mm in size. And the influences of fly-ash content fluctuations of sand pre-mixed with fly-ash were small on the accuracy of surface water measurement and properties of concrete using sand pre-mixed with fly-ash.
This study was designed to improve the resistance of sulfate attack of blast furnace slag cement by using anhydrite (AH) and lime stone powder (LSP) as a admixture. The early age (7day) hydration product and the porosity of the specimens are investigated for the explanation of the effect of AH replacement, LSP replacement and combined use on blast furnace slag cement against sulfate attack. As a result, the highest resistance against sulfate attack was found at 5% of AH and 20% of LSP replacement ratio in this study. In the case of combined use, high amount of ettringite, and monocarbonate are generated instead of monusulfate. Even more, the pore size was small. Only with replacing the AH, it was not effective for the sulfate attack, even increasing the amount of AH, generating of monosulfate was not restrained. Also only with the replacing of LSP, resistant was not improved, because the amount of ettringite was small, even if the monocarbonate was founded instead of monusulfate. Same tendency was observed with the mortal specimens for sulfate attack test.
The purpose of this study is to discover a method for improving the long term strength gain of steam cured cement pastes. Pastes of ordinary portland cement (OPC) and blended cement (containing 40% ground granulated blast furnace slag GGBFS) were cured at 60°C for 24 hours and subsequently stored in limewater at 20°C. The development of the microstructure in the cement paste was analyzed and studied using backscattered electron images and the hydration products formed inside the cement grains were classified by energy dispersive spectroscopy. The two main findings in this study are ; first, the microstructure shows the formation of coarser hollow shells and cement grains surrounded by inner C-S-H rims. The smaller cement grains hydrate completely and leave hollow shells. Precipitations of calcium monosulfoaluminate were observed within the structure. And second, the blended cement pastes see a reduction in the coarse hollow shells and thicker rims compared with the OPC pastes at the early stages of hydration. The Ca/Si ratio of the rim is lower than that of OPC pastes and its chemical composition changes during the curing time. Hydration products form as dispersed particles throughout the microstructure and then fill the capillary pores and hollow shells. It can be concluded that for blended cement pastes, calcium ions diffuse into the previously formed microstructures and precipitate as hydration products such as CH and C-S-H phases. Furthermore, the effects of using colloidal silica as an admixture to improve long-term strength were studied in order to determine if using a pozzolanic supplementary cementitious material can prevent the formation of thick rims around the cement grains.
High fly-ash paste, which has been applied to the fish reef or algal reef, has a complicated organizational structure with very small water-powder ratio. However, by the change in the water-powder ratio or mixing time, its properties are expected to be significantly affected. In this study, experimental investigations were carried out to assess the effect of manufacturing conditions in the properties of high fly-ash paste, such as strength, organizational structure and shrinkage of the paste, in the change of the water-powder ratio and mixing time. As a result, the following was obtained ; (1) strength and densification of the organization significantly increased with the extension of mixing time, but initial setting time hardly changed, (2) drying shrinkage strain was 2,000∼3,000μ at 2 weeks, and was settled 4weeks later, and tended to increase slightly with the mixing time, (3) autogenous shrinkage in the paste at young age is little.
Hardened cement composites constituted of cement, ground granulated blast furnace slag powder and blast slag furnace sand as fine aggregate are excellent sulfuric acid resistance because of forming white colored protective film based on calcium sulfate. Assuming these composites applied for the concrete structures under the severe acid circumstance such as sewerage and acid hot spring, the basic mechanical properties of strengths, modulus of elasticity, fracture energy, a coefficient of thermal expansion were investigated. The flexural strength of reinforced concrete beam was experimentally obtained by the four point bending tests and structural characteristics were discussed. Furthermore, the load test for reinforced concrete beam after soaking in the sulfuric acid were also carried out in order to apply the precast concrete products for practical infrastructures.
It has been known that durability of mortar is improved by addition of polymer. We assume that the addition of polymer is one of technologies about extension of life-span of concrete. Experimental studies about mechanical property, durability and property of drying shrinkage cracking of concrete added SBR were carried out. As a result, strength of concrete added SBR was the same degree or greater than normal concrete. Carbonation depth was decreased as the ratio of SBR were increased. Relative dynamic modulus of elasticity of the concrete added SBR under on resistance of freezing and thawing test was much the same of normal concrete added an air entraining agent. No cracks had occurred for 55days on drying shrinkage cracking test when SBR were added to 10% weight ratio of cement.
The main objective of this study is to clarify the influence of limestone aggregate on strength and drying shrinkage of concrete. Three kinds of limestone aggregates from different regions of Japan were used. The specimens were mixed with fine or coarse limestone and sandstone. As a result, the strengths and modulus of elasticity of concretes with limestone were larger than those of sandstone concretes. The drying shrinkage of concrete with fine or coarse limestone aggregate decreased clearly regardless of the region of production. Furthermore, the volume change of limestone aggregate in water and drying condition was quite smaller than that of sandstone aggregate. It is thought that the main cause of the reduction of drying shrinkage in concretes with limestone is the volume change of the aggregate itself.
It has been pointed out that the use of fly ash in concrete is effective in controlling the expansion due to ASR (alkali silica reaction). In Japan, the total amounts of alkalies in concrete has been kept up to 3.0kg/m3 as one of the major countermeasures for ASR suppression. Recently, it is reported that ASR may be accelerated by the steam curing of PCa concrete even in the case of low alkalies content of less than 3.0kg/m3. On the other hand, the effectiveness of fly ash on the suppression of ASR in concrete is often evaluated by means of the mortar bar method according to JIS A1146, however there are some problems that it takes the long time of 3 or 6 months in assessment, and that it can't take the pessimum content of reactive aggregate in mix proportions of mortar into considerations. In this study, the effectiveness of fly ash in steam-cured concrete was experimentally investigated. For this purpose, the steam-cured fly ash concrete with the replacement percentages by fly ashes was exposed to the accelerated test conditions which were selected as the factor, the temperature, the water supply, the immersion in saturated NaCl solution and so on. As the result of tests, it has been found that the accelerated condition exposed to the saturated NaCl solution at 50°C is most suitable as the rapid test method for the steam-cured fly ash concrete.
There exist large numbers of ASR-deteriorated bridges on the Noto expressway through the center of Noto peninsula in Ishikawa Prefecture. In some serious cases, a very severe deterioration which appears to directly be related with the reduction in load carrying capacity of structures has occurred; the significant decrease in compressive strength of concrete, the loss in bonding strength around steel reinforcement, and the fracture of steel reinforcement at the bent and so on. This study aims at investigating both the mix proportions of concrete and the rock type of reactive aggregates used in ASR-deteriorated bridges. Furthermore, the relationships between mechanical properties of cores taken from various portions of bridge pier and ASR degradation ranks classified by the various inspection were discussed for the purpose of the diagnosis and maintenance procedures of these bridges.
Long-Period Fiber Gratings (LPFGs) which have a periodic structure in the refractive index in the longitudinal direction of the fiber with a period of about 0.5 mm, convert incident light in the fundamental LP01 mode into higher-order LP0m modes through mode coupling. Because the higher-order modes cannot propagate in a single-mode fiber but are lost outside the fiber, an LPFG works as an attenuator. LPFGs with different Bragg wavelengths were fabricated by using the point exposure method in which the period was freely changed. Just after excimer laser light exposure, transmission spectra of LPFGs were measured. Furthermore, compared to the simulation, the higher-order modes of peaks in the transmission spectra of experimentally fabricated LPFGs were identified.
In the present paper, effects of titanium skin layer on impact damages in GFRP core of Ti/GFRP laminates as Fibre-Metal Laminates under impact loadings were investigated. Low-velocity impact tests using a drop-weight tower were conducted on Ti/GFRP laminates with single titanium layer as a face sheet. In these tests, the titanium skin or GFRP layer were considered to be as an impact surface, and damages in the GFRP layer after the impact loading were observed in each case. From the experimental evidence, it was found that out-of-plane deformation and internal damages of GFRP layer were constrained by the titanium layer which was set at the opposite side of impact. Furthermore, four-point bending tests were conducted using the GFRP core derived from Ti/GFRP laminates after impact loadings. Experimental results showed that the specimens impacted from the GFRP layer side exhibited superior residual bending strength and bending stiffness compared to those impacted from the titanium layer side. Numerical analyses of impact damages in Ti/GFRP laminates using a finite element method were executed in order to evaluate damage development in the GFRP layer. The calculated damage state in the GFRP layer agreed well with the experimental results. As a consequence, it was revealed that the titanium layer at the opposite side of impact plays a major role in preventing damages in the GFRP core under low-velocity impact loading on Ti/GFRP laminates.
Although the plastic strain induced in materials increases the mechanical strength, it may reduce the fracture toughness. The change in the fracture toughness is brought about by four factors; reduction in critical plastic strain due to pre-strain, localization of deformation, increase of material strength by work hardening, and change in material resistance for fracture. In this study, correlation between change in fracture toughness by pre-strain and the four factors was investigated. Firstly, the change in the tensile properties and fracture toughness were examined for pre-strained SM490 carbon steel. The specimens with blunt notch of 0.2 mm and 0.4 mm radius were used in addition to those with conventional fatigue pre-cracking. The degree of applied plastic strain was 5%, 10% and 20%. The fracture toughness was largest when the induced plastic strain was 5%, although it decreased in the cases for the plastic strain of 10% and 20%. Secondly, the stress and strain field near notch tip was evaluated by simulating the experiment using elastic-plastic finite element analyses. It was concluded that the change in fracture toughness was mainly brought about by the change in material resistance caused by the plastic strain. Under the plastic strain of 10% and 20%, the critical plastic strain for crack initiation decreased due to change in material resistance in addition to apparent reduction by pre-straining. The localized deformation and work hardening had minor effect on the change in fracture toughness.